As a conventional maintenance information output apparatus, known is an apparatus in which the life of a speed reducer is calculated and accumulated at each sampling time from the generated torque, number of rotations, and accumulated operation time of a servo motor for driving a robot manipulator of an industrial robot, and, when the accumulated value exceeds a predetermined reference value, the need for inspection or replacement of the speed reducer is displayed (for example, see Patent Reference 1).    Patent Reference 1: JP-A-7-124889 (pages 2 and 3, FIGS. 1 and 2)